Kramers-Kronig relation between nonlinear absorption and refraction of C(60) and C(70).

Using the Z-scan technique with 532 nm 16 picosecond laser pulses, we observe reverse saturable absorption and positive nonlinear refraction of toluene solutions of both C(60) and C(70). By deducting the positive Kerr nonlinear refraction of the solvent, we notice that the solute molecules contribute to nonlinear refraction of opposite signs: positive for C(60) and negative for C(70). Attributing nonlinear absorption and refraction of both solutes to cascading one-photon excitations, we illustrate that they satisfy the Kramers-Kronig relation. Accordingly, we attest the signs and magnitudes of nonlinear refraction for both solutes at 532 nm by Kramers-Kronig transform of the corresponding nonlinear absorption spectra.

Mass transport following impulsive optical excitation.

Transition from reverse-saturable absorption to saturable absorption of the chloroaluminum phthalocyanine solution excited by a giant laser pulse is ascribed not just to the saturation of excited state absorption, but also to the outward migration of the solute molecules at the laser beam center. While the saturation of excited state absorption occurs within a single picosecond laser pulse, the beam center population decrease is sustained much longer than the pulse duration. We distinguish these two mechanisms with the Z-scan technique, utilizing picosecond pulses with pulse-to-pulse separations ranging from 0.1 to 5.0 s.